US wholesaler Costco has reported a 10% rise in first-quarter profit, helped by the labour disputes in southern California, which led to increased numbers of shoppers at its warehouse clubs.

The company posted net income of US$160.2m, or 34 cents a share, for the quarter to 23 November, compared with $145.7m, or 31 cents a share, a year earlier. Analysts had been expecting earnings of 31 cents a share on average, reported Dow Jones News Service.

Costco said revenue rose 14% to $10.52bn, while same-store sales rose 11% and revenue from membership fees rose 13% to $211.7m.

Chief financial officer Richard Galanti said the grocery strikes and lockouts at Albertsons, Kroger's Ralphs and Safeway's Vons in southern California had boosted Costco's overall comparable sales by as much as one percentage point. The company also posted strong comparable sales rises in the Midwest and Northeast, and its international division continued to perform strongly, Galanti said.